1. Field of Invention
The invention relates to a one-axis starter apparatus in an internal combustion engine for automobiles, motor cycles or other fuel powered vehicles.
2. Description of Related Art
Generally, with this type of starter apparatus, known as an inertia sliding type or a so-called Bendix-type, a pinion gear engaged with a ring gear (driven gear) at the internal combustion engine side is directly provided at the tip end of a starter motor shaft via a helical spline. In line with the rotation drive of the Bendix-type starter motor, the starter motor is disengageably engaged with the pinion gear by inertia sliding (advancement and retreat) of the pinion gear on the starter motor shaft. However, in this Bendix-type, having engagement of the ring gear and the pinion gear, when the rotation at the ring gear exceeds that at the pinion gear, the pinion gear slides on the motor shaft by inertia, making a quick return and thereby risking an unstable or canceled engagement between the ring gear and the pinion gear. Therefore, a one-way rotation clutch is proposed to intervene between the pinion gear and the motor shaft to prevent the quick return of the pinion gear. Such a one-way rotation clutch, as shown in FIG. 4, is already known. A typical one-way rotation clutch is a roller type, in which a pinion gear 17a is formed at a clutch inner member 17 that is slidably externally fitted to the motor shaft 16. The roller type clutch has a helical spline 18a formed in the clutch outer member 18 to be fitted to a helical spline 16a located at the tip end of the motor shaft 16, whereby a clutch roller 19 intervenes between the clutch inner member 17 and the clutch outer member 18. In addition, in this type of one-way rotation clutch, where the rotation of the ring gear, i.e., the driven gear, exceeds that of the pinion gear 17a, the clutch roller is disconnected, whereby a quick return of the pinion gear 17a is prevented by avoiding rotation loads on the clutch outer member 18 while the clutch inner member 17 is permitted to rotate freely.
In prior art starter motors, the clutch device is expensive, resulting in increased production costs, as well as a cumbersome assembly process. Further, the prior art clutch devices require a bearing 20 that is pressure-fitted onto the inner circumferential surface of the clutch inner member 17 so that sliding is enabled between the clutch inner member 17 and the motor shaft 16. Further still, prior clutch devices require a motor shaft having an axial portion 16b with a smaller diameter than the diameter of the helical spline 16a formed at the tip of the motor shaft so that a gap is produced between the axial portion 16b and the helical spline 16a of the motor shaft. The shaping or cutting of the axial portion and helical spline of the motor shaft not only requires more work time, but also may negate the strength of the motor shaft 16. Therefore, to compensate for a lowering in strength, a material having high strength must be used or the motor shaft as a whole must be enlarged. This too results in increased production costs or an upsizing of the apparatus.
To overcome some of the problems of the prior art, as has been disclosed in Japanese Laid-Open Patent Publication No. 117166 of 1988, a one-axis starter apparatus that does not require any roller type one-way rotation clutch has been developed. This type of starter apparatus uses a friction member and is composed of a friction plate by which an outer member, having a pinion gear formed therein, is externally fitted to an inner member provided with a helical spline fitted to the motor shaft, and which friction member intervenes between the inner member and outer member. A coned disk spring resiliently presses the outer member to the friction member side. However, in this friction member type starter apparatus, where rotation of the outer member exceeds that of the inner member, the outer member rotates idly against the friction force of the friction member, to prevent the inner member from a quick return along with the outer member. As described above, this friction member type starter apparatus eliminates the need of any roller type one-way rotation clutch. But, it is also requires making the tip end of the motor shaft smaller in diameter so that the inner circumferential surface on which a helical spline is formed does not interfere with the motor shaft where the inner member slides toward the tip end. Thus, as in the related art set forth in the above description, the problems of increased production costs due to increased machining time of the differently diametered motor shaft or due to the necessity of increasing the size and strength of the motor shaft or its materials in the alternative still remain.
The invention has been developed to solve the problems identified in view of the above situations. The invention relates to a one-axis starter apparatus having an inner member fitted externally to a motor shaft of a starter motor via a first helical spline so as to freely advance and retreat, and having an outer member on which a pinion gear is disengageably engaged with a driven ring gear on the basis of the advance and retreat of said inner member, and which outer member is externally fitted thereto, wherein the outer member is pressed toward the driven ring gear by a pressing means in a state where its movement towards the driven ring gear is regulated with respect to the inner member, and is externally fitted to the inner member via a second helical spline reversely oriented from the first helical spline.
With the above construction, an impact due to engagement with the ring gear can be lightened, and a quick return of the pinion gear can be prevented. A quick return preventing means, such as a one-way rotation clutch, is therefore not required.
In the starter apparatus thus structured, the first helical spline of the motor shaft according to the invention is provided to the tip end of the motor shaft beyond the area where the inner member freely advances and retreats, whereby the cutting of the motor shaft is simplified, and there is no problem in which the strength of the motor shaft is lowered due to provision of an axial portion having a smaller diameter than the helical spline portion.
Further, in the starter apparatus, the pressing means according to the invention may be composed of two overlapped coned disk springs.